1. Field of the Invention
The present invention relates to a multiblade blower installed in an air conditioning system for a vehicle, and the like.
2. Description of the Related Art
A multiblade blower includes an impeller having a plurality of blades placed circumferentially around a rotation shaft, and when the impeller is rotated, air is taken in from a side of an inner diameter end portion of the blade, and is discharged from a side of an outer diameter end portion thereof. A blower performance such as air blowing ability and noise of the multiblade blower is influenced by the shapes of the blades and the shape of a casing for housing the impeller, and the like. Since the length in an air flowing direction of each of the blades is short in the multiblade blower, an air flow flowing along the blade is difficult to form, and a vortex flow occurs due to separation of the air flow. This vortex flow reduces the air blowing ability, and is a main cause of the noise.
In order to solve the above problems, the applicant filed the application of the multiblade blower shown in FIG. 5 and FIG. 6 (Japanese Patent Application No. 2001-384139). FIG. 5 shows an impeller 1 of the multiblade blower, and FIG. 6 shows blades 2 section encircled by the alternate long and short dash line in FIG. 5.
The impeller 1 includes a number of blades 2 circumferentially with a central rotation shaft as its center as shown in FIG. 5, and when the blades 2 rotate around the rotation shaft, air is taken in from sides of inner diameter end portions 2a of the blades 2 and is discharged from sides of outer diameter end portions 2b. 
Here, the blade 2 is in a wing shape at the side of the inner diameter end portion 2a (a front half part of the blade 2). Namely, it is in a shape in which the thickness of the blade gradually increases once, and thereafter, gradually decreases. The shape of the front half part of the blade 2 restrains disturbance of an air flow. The thickness of the blade 2 at the side of the outer diameter end portion 2b (a rear half part of the blade 2) is substantially uniform and linear. Due to this, the separation of air at the rear half part of the blade 2 is restrained, and occurrence of a vortex flow at the wake flow behind the blade 2 is restrained.
However, in the multiblade blower described in the aforementioned application, the outer diameter end portion 2b of each of the adjacent blades 2 is placed to be somewhat spaced from each other, and therefore as shown in FIG. 6, there arises the possibility that air flowing to a suction surface of the outer diameter end portion 2b is deviated to a pressure surface of the other adjacent blade 2 to form a shearing flow 3 behind the blade 2.
In order to solve the above-described problems, a method for forcefully restraining a deviating flow of air by forming a space between the outer diameter end portions 2b of the adjacent blades 2 to be small can be considered.
However, pressure recovery becomes insufficient by the increase in relative velocity of air flowing between the outer diameter end portions 2b, and there is the possibility that air blowing performance and noise property are reduced at operating points with high pressure loss.